BEIJING -- China issued a stiff protest Sunday over an updated U.S.-Japanese strategic agreement, saying its reference to Taiwan violates China's national sovereignty and its criticism of China's military buildup is "untenable."

The complaint, issued by the Foreign Ministry, reflected deep government concern over Japan's evolving decision to lean toward closer security cooperation with the United States in East Asia, including on the issue of Taiwan. Although Japan has not spelled out what military assistance it might provide, to Chinese ears the accord sounded like a promise to help the United States defend Taiwan in the event of war.

"The statement included the Taiwan issue, which relates to China's sovereignty, territorial integrity and national security," said Kong Quan, the chief ministry spokesman. "The Chinese government and people strongly oppose this statement."

The revised U.S.-Japanese strategic understanding, issued Saturday after a meeting of Secretary of State Condoleezza Rice and Defense Secretary Donald H. Rumsfeld with their Japanese counterparts, for the first time included security in the area around Taiwan as a "common strategic objective."

The U.S.-Japanese statement also drew attention to China's rapid military modernization program, calling it a matter of concern, and urged Beijing to be more transparent in its military planning and weapons procurement. The focus on China's military improvements also drew sharp criticism in Sunday's statement from Beijing.

Tensions have been rising recently between China and Japan. Public animosity has focused on overlapping claims to exclusive economic zones in the East China Sea. Privately, a senior diplomat pointed out, Chinese officials have expressed increasing concern over Japan's apparent willingness to cooperate more closely with the United States in the defense of key waters north of Taiwan.

The United States has pledged to help in the defense of Taiwan, potentially including the dispatch of military forces to counter any attack by China across the Taiwan Strait. Japanese help in defending the sea lanes north of Taiwan would be of great value to the U.S. military if the U.S. Navy were ordered into the area.